More than one-third of the average American woman's 78-year lifespan is lived in the postmenopausal stage of life, a time associated with increased risk of coronary artery disease, osteoporosis, and endometrial/breast cancer. Currently, there are over 40 million women over the age of 50 in the United States - a large segment of the population at high risk for these medical problems. During the last two decades, the benefits and risks of postmenopausal estrogen replacement have been the subject of considerable debates within the scientific community. Although estrogen therapy has been shown unequivocally to retard bone thinning and fractures, it has also been associated with an increase in endometrial and breast cancer, gallstones and, in some cases, an increased risk of coronary artery disease. On the other hand, coronary artery disease increases in both frequency and severity after menopause, an increase which may be related to lipoprotein changes induced by the decline of estrogen levels. Recent evidence indicates that postmenopausal estrogen users have only one-third the mortality of non-users and that users of estrogen-progesterone combinations have less endometrial cancer than non-users or those using estrogen alone. This is a proposal to study prospectively the changes effected in circulating lipoproteins/apoprotein levels and selected parameters of coagulation by the administration of two doses of conjugated equine estrogen, alone and in combination with a progestogen. The regimens used by this study have been shown clinically to protect both the endometrium from hyperplasia and cancer and bones from osteoporosis. Therefore, it is hoped that an even further refinement of optimal hormone replacement therapy can be achieved, one which also produces the most beneficial dose-response relationships between estrogen and lipoprotein level, as well as coagulation factors.